file-operations: Fix crashes when extracting encrypted archives

When extracting encrypted archives, Nautilus randomly crashes when opening
the password dialog. This happens pretty often under X11, but I have
already seen a few crashes on Wayland as well. I suppose that all those
crashes are caused because the password dialog is constructed on the
extraction thread and GTK is not thread-safe. Let's modify the code to call
GTK on the main thread only to fix those crashes.

Fixes: https://gitlab.gnome.org/GNOME/nautilus/-/issues/1825